From the viewpoint of conserving the global environment, the need to reduce nitrogen oxides (NOx), black smoke, particles and other emissions contained in the exhaust gas of internal combustion engines, including among others diesel engines, is posing a major challenge.
One of the known means for addressing the emission problem according to the prior art is a pressure-storage type (a common rail type) high pressure fuel injection device capable of injecting a constant quantity of fuel independent of the engine speed, controlling the injection pressure and the injection timing independent of each other, and easily performing split injection (pilot injection). Whereas this pressure-storage type high pressure fuel injection device has a two stage fuel injection valve using a small on/off electromagnetic valve as a pilot valve, as it uses a stationary orifice for controlling the hydraulic force to open and close the needle valve, the injection rate pattern (the shape of the graphically expressed injection rate, i.e. the waveform representing variations in the injection rate over time) is a fixed rectangle, and a steep rise of the initial injection volume leads to an increase in nitrogen oxide (NOx) emission.
In order to effectively reduce harmful substances in exhaust gas, it is necessary to elaborately control the injection rate by not only regulating the fixed injection rate but also by selecting the optimal injection rate pattern according to variations in the engine speed, engine load level and common rail pressure.